The project has now been released as GPL open-source software on SourceForge.
From
TheCurves’ project pages,
you can download TheCurves and complain to me about it if you like.

If you don’t know the meaning of the term “parameterized family of curves”,
and don’t mean to find out, you may find this application amusing,
but it will be of little use to you.

When the program is run as an applet in a web page, the plot parameters and
formulas are configurable by HTML and dynamically scriptable, so that the
applet can be initialized to present a specific plot when the page is opened,
or to change plots when the user clicks on a control in the web page.

Some initial notes on how to use TheCurves may be found in the document
Using TheCurves.

The program uses the 3plus4 expression parser by Stefan Matthias Aust, which
is explicitly made available for inclusion with in GPL’ed projects. See
3plus4 Java.